<%-- 
    Document   : image
    Created on : 2016-6-4, 16:06:12
    Author     : Administrator
--%>
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@ page contentType="image/jpeg"
	import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"%>
<%!Color 
        getRandColor(int fc, int bc) 
        {//给定范围获得随机颜色
		Random random = new Random();
		if (fc > 255)
			fc = 255;
		if (bc > 255)
			bc = 255;
		int r = fc + random.nextInt(bc - fc);
		int g = fc + random.nextInt(bc - fc);
		int b = fc + random.nextInt(bc - fc);
		return new Color(r, g, b);
	}%>
<%
    
	//设置页面不缓存
	response.setHeader("Pragma", "No-cache");
	response.setHeader("Cache-Control", "no-cache");
	response.setDateHeader("Expires", 0);
	// 在内存中创建图象
	int width = 70, height = 20;
	BufferedImage image = new BufferedImage(width, height,
			BufferedImage.TYPE_INT_RGB);
	// 获取图形上下文
	Graphics g = image.getGraphics();

	//生成随机类
	Random random = new Random();

	// 设定背景色
	g.setColor(getRandColor(200, 250));
	g.fillRect(0, 0, width, height);

	//设定字体
	g.setFont(new Font("宋体", Font.PLAIN, 18));

	//画边框
	g.setColor(Color.black);
	g.drawRect(0, 0, width - 1, height - 1);

	// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
	g.setColor(getRandColor(160, 200));
	for (int i = 0; i < 155; i++) {
		int x = random.nextInt(width);
		int y = random.nextInt(height);
		int xl = random.nextInt(12);
		int yl = random.nextInt(12);
		g.drawLine(x, y, x + xl, y + yl);
	}

	char[] cs = new char[] { '1', '2', '3', '4', '5', '6', '7', '8',
			'9', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'A',
			'B', 'M' };
        
	// 取随机产生的认证码(4位数字)
	//StringBuffer sRand=null;
        String sRand="";
	for (int i = 0; i < 4; i++) {
            char c = cs[random.nextInt(cs.length)];
            String rand = new Character(c).toString();
            //sRand.append(rand);
            sRand += rand;
            // 将认证码显示到图象中
            g.setColor(new Color(20 + random.nextInt(110), 20 + random
                            .nextInt(110), 20 + random.nextInt(110)));
            //调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
            g.drawString(rand, 13 * i + 6, 16);
	}
        
	// 将认证码存入session
	session.setAttribute("srand", sRand); //这行代码使我们关注的重点 

	// 图象生效
	g.dispose();

	// 输出图象到页面
	try {
		ImageIO.write(image, "JPEG", response.getOutputStream());
	} catch (Exception e) {
		e.getMessage();
	} finally {

		//解决以调用错误
		out.clear();
		out = pageContext.pushBody();
	}
%>
